Systems and Methods for Detecting Microannulus Formation and Remediation

ABSTRACT

Optical analysis systems may be useful in detecting microannulus formation in a wellbore casing and remediating a microannulus. In some instances, a system may include a cement sheath disposed about and in contact with at least a portion of an exterior surface of a casing; and at least one optical computing device arranged coupled to the casing, the at least one optical computing device having at least one integrated computational element configured to optically interact with a material of interest and thereby generate optically interacted light, and at least one detector arranged to receive the optically interacted light and generate an output signal corresponding to a characteristic of the material of interest, the material of interest comprising at least one selected from the group consisting of the cement sheath, a displacement composition disposed between the cement sheath and the exterior surface of the casing, and any combination thereof.

BACKGROUND

The present invention relates to optical analysis systems and methods for analyzing wellbore casings, and in particular, systems and methods for detecting microannulus formation in a wellbore casing and remediating a microannulus.

In constructing a wellbore, a cement slurry is typically placed in the annular volume between the exterior of the casing and the wall of the wellbore that, once hardened, forms a cement sheath. The cement sheath, inter alia, supports the casing and prevents fluids from migrating between the various zones of the wellbore. In some instances, the bond between the cement sheath and casing can fail. This failure can produce a very thin annular space, known as a microannulus, between the exterior surface of the casing and the cement sheath.

The microannulus can permit fluids to migrate between zones of the subterranean formation, which can reduce the quality and efficiency of production operations. Further, a microannulus can serve as a starting point for more significant failures in the casing, including those that lead to portions of the wellbore collapsing.

A microannulus can form for many reasons including, for example, fluctuations in temperature and pressure in a wellbore after formation of the cement sheath.

A cement bond log is one of the methods used to determine if a microannulus has formed. Because a casing that is bonded to a cement sheath attenuates sound differently than a casing that is not bonded thereto, a cement bond log uses sonic-type tools to measure amplitude variations in acoustic signals. Typically, cement bond logs are run shortly after formation of the cement sheath. After other wellbore operations have begun, analysis for microannulus formation often requires shutting down production and performing another cement bond log, thereby increasing nonproductive time and costs. Accordingly, systems and methods for detecting microannulus formation with minimal downtime would be of value.

SUMMARY OF THE INVENTION

The present invention relates to optical analysis systems and methods for analyzing wellbore casings, and in particular, systems and methods for detecting microannulus formation in a wellbore casing and remediating a microannulus.

One embodiment of the present invention is a system that comprises a cement sheath disposed about and in contact with at least a portion of an exterior surface of a casing; and at least one optical computing device arranged on the casing, the at least one optical computing device having at least one integrated computational element configured to optically interact with a material of interest and thereby generate optically interacted light, and at least one detector arranged to receive the optically interacted light and generate an output signal corresponding to a characteristic of the material of interest, the material of interest comprising at least one selected from the group consisting of the cement sheath, a displacement composition disposed between the cement sheath and the exterior surface of the casing, and any combination thereof.

Another embodiment of the present invention is a system that comprises a cement sheath disposed about and in contact with at least a portion of an exterior surface of a casing; and at least one integrated computational element configured to optically interact with a material of interest and thereby generate optically interacted light, and at least one detector arranged to receive the optically interacted light and generate an output signal corresponding to a characteristic of the material of interest, the material of interest comprising at least one selected from the group consisting of the cement sheath, a displacement composition disposed between the cement sheath and the exterior surface of the casing, and any combination thereof.

Yet another embodiment of the present invention is a method that comprises optically interacting a material of interest and at least one integrated computational element, thereby generating an output signal corresponding to a characteristic of the material of interest, the material of interest comprising at least one selected from the group consisting of a cement sheath disposed about and in contact with at least a portion of an exterior surface of a casing, a displacement composition disposed between the cement sheath and the exterior surface of the casing, and any combination thereof.

The features and advantages of the present invention will be readily apparent to those skilled in the art upon a reading of the description of the preferred embodiments that follows.

BRIEF DESCRIPTION OF THE DRAWINGS

The following figures are included to illustrate certain aspects of the present invention, and should not be viewed as exclusive embodiments. The subject matter disclosed is capable of considerable modifications, alterations, combinations, and equivalents in form and function, as will occur to those skilled in the art and having the benefit of this disclosure.

FIG. 1 illustrates an exemplary integrated computational element, according to one or more embodiments.

FIG. 2 illustrates a block diagram non-mechanistically illustrating how an optical computing device distinguishes electromagnetic radiation related to a characteristic of interest from other electromagnetic radiation, according to one or more embodiments.

FIGS. 3A-B illustrate an exemplary system for monitoring a cement sheath, according to one or more embodiments.

FIG. 4 illustrates an exemplary system for monitoring a cement sheath, according to one or more embodiments.

DETAILED DESCRIPTION

The present invention relates to optical analysis systems and methods for analyzing wellbore casings, and in particular, systems and methods for detecting microannulus formation in a wellbore casing and remediating a microannulus.

The exemplary systems and methods described herein employ various configurations of optical computing devices, also commonly referred to as “opticoanalytical devices,” for detecting indicators of microannulus formation, e.g., pulling away of a cement sheath from a casing and/or infiltration of displacement compositions between a cement sheath and a casing. For example, the optical computing devices, which are described in more detail below, may advantageously provide real-time or near real-time monitoring of a cement sheath and/or the infiltration of a displacement composition, which can be indicative of microannulus formation. In another example, the optical computing devices may advantageously provide monitoring of a cement sheath and/or infiltration of a displacement composition over an extended time period (e.g., weeks to months to years, depending on the application), where the data is stored locally with the optical computing devices and retrieved when desired. In this example, long-term monitoring for microannulus formation may advantageously be utilized in a cement sheath health analysis. In either example, monitoring and analyzing for microannulus formation may be used in determining the parameters, e.g., location and size, of remedial operations like cement squeeze operations.

The disclosed systems and methods may be suitable for use in the oil and gas industry since the described optical computing devices provide a relatively low cost, rugged, and accurate means for monitoring materials of interest, e.g., a cement composition and/or fluids. It will be appreciated, however, that the various disclosed systems and methods are equally applicable to other technology fields including, but not limited to, industrial applications, mining industries, CO₂ injection well applications, and any field where it may be advantageous to analyze for microannulus formation.

As used herein, the term “cement” refers to a hardenable material suitable for use to seal off an annular space in a wellbore. Cement is not necessarily hydraulic cement, since other types of materials (e.g., epoxies, latexes, and bentonites) can be used in place of, or in addition to, a hydraulic cement. As used herein, the term “hydraulic cement” refers to a cement that hardens in the presence of water. Exemplary examples of cements may include, but are not limited to, Portland cement, gypsum cements, calcium phosphate cements, high alumina content cements, silica cements, high alkalinity cements, shale cements, acid/base cements, magnesia cements such as Sorel cements, fly ash cements, zeolite cement systems, cement kiln dust cement systems, slag cements, micro-fine cements, and the like, any derivative thereof, and any combination thereof. Cement compositions described herein may harden by hydrating, by passage of time, by application of heat, by cross-linking, and/or by any other technique, method, or means.

As used herein, the term “cement sheath” refers to a cement composition disposed about and in contact with at least a portion of an exterior surface of a casing.

As used herein, the terms “remedial methods” or “remedial operations” refer to procedures carried out in subterranean formations or in wellbores penetrating the formations to correct problems such as cementing a microannulus (e.g., cement squeeze operations), sealing leaks, cracks or voids, placing plugs in the wellbore or in zones or formations containing undesirable fluids, placing temporary plugs in lieu of packers to isolate zones or formations, filling external casing packers, and the like.

As used herein, the term “displacement composition” refers to a composition that congregates in the microannulus after the microannulus has been formed. Displacement compositions may include, but are not limited to, native wellbore fluids, treatment fluids, and any combination thereof. Displacement compositions can include various liquids, gases, mixtures thereof, and compositions having solids suspended therein.

As used herein, the term “fluid” refers to any substance that is capable of flowing, including, but not limited to, particulate solids, liquids, gases, foams, slurries, emulsions, powders, muds, glasses, and the like, and any combination thereof. Exemplary examples of displacement compositions may include, but are not limited to, aqueous-based fluids (e.g., water or brines), oleaginous-based fluids (e.g., organic compounds, hydrocarbons, oil, a refined component of oil, or petrochemical products), gases (e.g., air, nitrogen, carbon dioxide, hydrogen sulfide (H₂S), argon, helium, methane, ethane, butane, or other hydrocarbon gases), and the like, and any combination thereof.

As used herein, the term “electromagnetic radiation” refers to radio waves, microwave radiation, infrared and near-infrared radiation, visible light, ultraviolet light, X-ray radiation, and gamma ray radiation.

As used herein, the term “optical computing device” refers to an optical device that is configured to receive an input of electromagnetic radiation from a material of interest or sample of the material of interest, and produce an output of electromagnetic radiation from a processing element arranged within the optical computing device. The processing element may be, for example, an integrated computational element (“ICE”) used in the optical computing device. As discussed in greater detail below, the electromagnetic radiation that optically interacts with the processing element is changed so as to be readable by a detector, such that an output of the detector can be correlated to at least one characteristic of the material of interest being measured or monitored. The output of electromagnetic radiation from the processing element can be reflected electromagnetic radiation, transmitted electromagnetic radiation, and/or dispersed electromagnetic radiation. Whether reflected or transmitted, electromagnetic radiation analyzed by the detector may be dictated by the structural parameters of the optical computing device as well as other considerations known to those skilled in the art. In addition, emission and/or scattering by the material of interest (e.g., via fluorescence, luminescence, Raman scattering, and/or Raleigh scattering) can also be monitored by the optical computing devices.

As used herein, the term “optically interact” or variations thereof refers to the reflection, transmission, scattering, diffraction, or absorption of electromagnetic radiation either on, through, or from one or more processing elements (i.e., integrated computational elements). Accordingly, optically interacted light refers to light that has been reflected, transmitted, scattered, diffracted, or absorbed by, emitted, or re-radiated, for example, using the integrated computational elements, but may also apply to interaction with a material of interest (e.g., a cement sheath and/or a displacement composition).

As described above, a microannulus, a small gap between a casing and the surrounding cement sheath, may form, at least in part, because of fluctuations in temperature and pressure in a wellbore after formation of the cement sheath. It should be noted that the term “casing” encompasses any tubular structure used to contain a fluid, which may include, but are not limited to, liners, pipes, conduits, and the like.

Formation of a microannulus can lead to, inter alia, changes in the properties of the cement sheath, infiltration of a displacement composition into the microannulus, and the like. Accordingly, the characteristics of a cement sheath and/or characteristics of a displacement composition that infiltrates a microannulus may, in some embodiments, be related to indicators of the potential formation of a microannulus. Exemplary examples of microannulus indicators may, in some embodiments, include, but are not limited to, the presence of a displacement composition, porosity changes of a cement sheath, temperature changes of a cement sheath, pH level of the material of interest, decreased output signal relating to the characteristic of interest, changes to the chemical composition of the cement sheath, and any combination thereof. For example, an optical computing device configured to measure a characteristic of the cement sheath may yield an output signal (described in more detail herein) in response to, inter alia, the cement sheath having pulled away from the casing as the interacted light (described in more detail herein) has a longer distance to travel and/or a displacement composition becomes disposed between the optical computing device and the cement sheath and also interacts with the displacement composition.

The exemplary systems and methods described herein may, in some embodiments, include at least one optical computing device coupled to or otherwise arranged adjacent to a casing and configured to measure at least one characteristic of a cement sheath and/or a displacement composition.

As used herein, the term “characteristic” refers to a chemical, mechanical, or physical property (quantitative or qualitative) of a material of interest (e.g., a cement sheath, a displacement composition, or analyte thereof). As used herein, the term “analyte” refers to a chemical component. The term analyte encompasses chemical components that are at least one of: present in the material of interest, may be added to the material of interest, involved in a chemical reaction (e.g., reagents and products) transpiring within the material of interest, and not involved in a chemical reaction transpiring within the material of interest. Illustrative characteristics that can be monitored with the optical computing devices disclosed herein can include, for example, chemical composition (e.g., identity and concentration in total or of individual analytes), impurity content, pH, viscosity, density, ionic strength, total dissolved solids, salt content, porosity, opacity, bacteria content, particle size distribution, color, temperature, hydration level, oxidation state, and the like. Moreover, the phrase “characteristic of interest” may be used herein to refer to a characteristic of a material of interest or analyte thereof.

Exemplary analytes may include, but are not limited to, water, salts, minerals (wollastonite, metakaolin, and pumice), cements (Portland cement, gypsum cements, calcium phosphate cements, high alumina content cements, silica cements, and high alkalinity cements), fillers (e.g., fly ash, fume silica, hydrated lime, pozzolanic materials, sand, barite, calcium carbonate, ground marble, iron oxide, manganese oxide, glass bead, crushed glass, crushed drill cutting, ground vehicle tire, crushed rock, ground asphalt, crushed concrete, crushed cement, ilmenite, hematite, silica flour, fume silica, fly ash, elastomers, polymers, diatomaceous earth, a highly swellable clay mineral, nitrogen, air, fibers, natural rubber, acrylate butadiene rubber, polyacrylate rubber, isoprene rubber, chloroprene rubber, butyl rubber, brominated butyl rubber, chlorinated butyl rubber, chlorinated polyethylene, neoprene rubber, styrene butadiene copolymer rubber, sulphonated polyethylene, ethylene acrylate rubber, epichlorohydrin ethylene oxide copolymer, ethylene propylene rubber, ethylene propylene diene terpolymer rubber, ethylene vinyl acetate copolymer, fluorosilicone rubber, silicone rubber, poly-2,2,1-bicycloheptene (polynorborneane), alkylstyrene, crosslinked substituted vinyl acrylate copolymer, nitrile rubber (butadiene acrylonitrile copolymer), hydrogenated nitrile rubber, fluoro rubber, perfluoro rubber, tetrafluoroethylene/propylene, starch polyacrylate acid graft copolymer, polyvinyl alcohol cyclic acid anhydride graft copolymer, isobutylene maleic anhydride, acrylic acid type polymer, vinylacetate-acrylate copolymer, polyethylene oxide polymer, carboxymethyl cellulose polymer, starch-polyacrylonitrile graft copolymer, polymethacrylate, polyacrylamide, and non-soluble acrylic polymer), hydrocarbons, acids, acid-generating compounds, bases, base-generating compounds, biocides, surfactants, scale inhibitors, corrosion inhibitors, gelling agents, crosslinking agents, anti-sludging agents, foaming agents, defoaming agents, antifoam agents, emulsifying agents, de-emulsifying agents, iron control agents, proppants or other particulates, gravel, particulate diverters, salts, cement slurry loss control additives, gas migration control additives, gases, air, nitrogen, carbon dioxide, hydrogen sulfide (H₂S), argon, helium, hydrocarbon gases, methane, ethane, butane, catalysts, clay control agents, chelating agents, corrosion inhibitors, dispersants, flocculants, scavengers (e.g., H₂S scavengers, CO₂ scavengers, or O₂ scavengers), lubricants, breakers, delayed release breakers, friction reducers, bridging agents, viscosifiers, weighting agents, solubilizers, rheology control agents, viscosity modifiers, pH control agents (e.g., buffers), hydrate inhibitors, relative permeability modifiers, diverting agents, consolidating agents, fibrous materials, bactericides, tracers, probes, nanoparticles, paraffin waxes, asphaltenes, foams, sand or other solid particles, and the like. Combinations of these components can be used as well. By way of nonlimiting example, the characteristic of interest of a displacement composition may be methane concentration, and increased methane concentration (e.g., from essentially no methane to a detectable concentration of methane) may indicate the formation of a microannulus.

In some embodiments, a material of interest may comprise an analyte (e.g., a tracer analyte and/or a probe analyte) having the primary purpose of being analyzed by optical computing devices described herein so as to indicate microannulus formation. For example, a probe analyte may be included in a cement composition used to form the cement sheath, and a system may comprise an optical computing device for measuring, for example, the fluorescence of the probe. In some embodiments, the probe may be sensitive to the presence of a gas, e.g., carbon dioxide. Accordingly, in the presence of a gas to which it is sensitive, the fluorescence intensity may decrease, which may be an indicator of microannulus formation. In another example, a tracer analyte may be included in a variety of wellbore fluids, and a system detecting the presence of the tracer analyte may indicate wellbore fluid is displacing the cement sheath, i.e., microannulus formation.

In some embodiments, systems and methods described herein may include at least one optical computing device coupled to a casing and configured to measure a characteristic of a material of interest (e.g., a cement sheath and/or a displacement composition). In some embodiments, the optical computing device may be disposed on the exterior surface of the casing. In other embodiments, the optical computing device may be integrated into the wall of the casing and otherwise arranged flush with the exterior surface of the casing. In yet other embodiments, the optical computing device may be integrated into the wall of the casing and extending outwardly beyond the exterior surface of the casing. Combinations and/or hybrids of the foregoing integration arrangements may be suitable in some embodiments. Integration into the wall of the casing may include, but is not limited to, mechanically coupling the optical computing device to or into a recessed portion of the wall using means such as, but not limited to, mechanical fasteners, press fitting, snap fitting, adhesives, welding or brazing techniques, and the like, and any combination thereof. It should be noted that the embodiments described herein relative to optical computing devices coupled to casings can be extended to optical computing devices couple to a downhole apparatus that is used in conjunction with a casing that is similarly capable of having a microannulus form at a surface, e.g., a centralizer, a casing shoe, or a collar (e.g., a float collar, a casing collar, a or landing collar), without departing from the scope of the disclosure.

Each optical computing device may include an electromagnetic radiation source, at least one processing element (e.g., integrated computational elements), and at least one detector arranged to receive optically interacted light from the at least one processing element. In some embodiments, the exemplary optical computing devices may be specifically configured for detecting, analyzing, and quantitatively measuring a particular characteristic of the material of interest. In other embodiments, the optical computing devices may be general purpose optical devices, with post-acquisition processing (e.g., through computer means) being used to specifically detect the characteristic of the material of interest.

In some embodiments, suitable structural components for the exemplary optical computing devices are described in commonly owned U.S. Pat. No. 6,198,531 entitled “Optical Computational System;” U.S. Pat. No. 6,529,276 entitled “Optical Computational System;” U.S. Pat. No. 7,123,844 entitled “Optical Computational System;” U.S. Pat. No. 7,834,999 entitled “Optical Analysis System and Optical Train;” U.S. Pat. No. 7,911,605 entitled “Multivariate Optical Elements for Optical Analysis System;” U.S. Pat. No. 7,920,258 entitled “Optical Analysis System and Elements to Isolate Spectral Region;” and U.S. Pat. No. 8,049,881 entitled “Optical Analysis System and Methods for Operating Multivariate Optical Elements in a Normal Incidence Orientation;” each of which is incorporated herein by reference in its entirety, and U.S. patent application Ser. No. 12/094,460 entitled “Methods of High-Speed Monitoring Based on the Use of Multivariate Optical Elements;” Ser. No. 12/094,465 entitled “Optical Analysis System for Dynamic Real-Time Detection and Measurement;” and Ser. No. 13/456,467 entitled “Imaging Systems for Optical Computing Devices;” each of which is also incorporated herein by reference in its entirety. As will be appreciated, variations of the structural components of the optical computing devices described in the above-referenced patents and patent applications may be suitable, without departing from the scope of the disclosure, and therefore, should not be considered limiting to the various embodiments or uses disclosed herein.

The optical computing devices described in the foregoing patents and patent applications combine the advantage of the power, precision, and accuracy associated with laboratory spectrometers, while being extremely rugged and suitable for field use. Furthermore, the optical computing devices can perform calculations (analyses) in real-time or near real-time without the need for time-consuming sample processing. In this regard, the optical computing devices can be specifically configured to detect and analyze particular characteristics of the material of interest. As a result, interfering signals are discriminated from those of interest of the material of interest by appropriate configuration of the optical computing devices, such that the optical computing devices provide a rapid response regarding the characteristics of interest as based on the detected output. In some embodiments, the detected output can be converted into a voltage that is distinctive of the magnitude of the characteristic being monitored, e.g., the concentration of methane that may increase (or go from essentially zero to a positive value) when a displacement composition that comprises methane is present. The foregoing advantages and others make the optical computing devices particularly well-suited for field and downhole use, but may equally be applied to several other technologies or industries, without departing from the scope of the disclosure.

The optical computing devices can be configured to detect not only the composition and concentrations of the material of interest, but they also can be configured to determine physical properties and other characteristics of the material of interest as well, based on their analysis of the electromagnetic radiation received from the particular material of interest. These physical properties and other characteristics may be used as determining microannulus indicators. For example, porosity increases may, in some embodiments, indicate that a microannulus has formed and been infiltrated by a corrosive composition that corrodes the cement sheath.

As will be appreciated, the optical computing devices may be configured to detect as many characteristics of the material of interest as desired. All that is required to accomplish the monitoring of multiple characteristics is the incorporation of suitable processing and detection means within the optical computing device for each characteristic. In some embodiments, the properties of the material of interest can be a combination of the properties thereof (e.g., a linear, non-linear, logarithmic, and/or exponential combination). Accordingly, the more characteristics that are detected and analyzed using the optical computing devices, the more accurately the properties of the material of interest will be determined.

The optical computing devices described herein utilize electromagnetic radiation to perform calculations, as opposed to the hardwired circuits of conventional electronic processors. When electromagnetic radiation interacts with a material of interest, unique physical and chemical information about the material of interest may be encoded in the electromagnetic radiation that is reflected from, transmitted through, or radiated from the material of interest. This information is often referred to as the spectral “fingerprint” of the material of interest. The optical computing devices described herein are capable of extracting the information of the spectral fingerprint of multiple characteristics of interest, and converting that information into a detectable output regarding the overall properties of material of interest. That is, through suitable configurations of the optical computing devices, electromagnetic radiation associated with characteristics of interest can be separated from electromagnetic radiation associated with all other analytes of the material of interest in order to estimate the properties of the material of interest in real-time or near real-time.

The processing elements used in the exemplary optical computing devices described herein may be characterized as integrated computational elements (ICE). Each ICE is capable of distinguishing electromagnetic radiation related to the characteristic of interest from electromagnetic radiation related to other substances. Referring to FIG. 1, illustrated is an exemplary ICE 100 suitable for use in the optical computing devices used in the systems and methods described herein. As illustrated, the ICE 100 may include a plurality of alternating layers 102 and 104, such as silicon (Si) and SiO₂ (quartz), respectively. In general, these layers 102, 104 consist of materials whose index of refraction is high and low, respectively. Other examples might include niobia and niobium, germanium and germania, MgF, SiO_(x), and other high and low index materials known in the art. The layers 102, 104 may be strategically deposited on an optical substrate 106. In some embodiments, the optical substrate 106 is BK-7 optical glass. In other embodiments, the optical substrate 106 may be another type of optical substrate, such as quartz, sapphire, silicon, germanium, zinc selenide, zinc sulfide, or various plastics such as polycarbonate, polymethylmethacrylate (PMMA), polyvinylchloride (PVC), diamond, ceramics, combinations thereof, and the like.

At the opposite end (e.g., opposite the optical substrate 106 in FIG. 1), the ICE 100 may include a layer 108 that is generally exposed to the environment of the device or installation. The number of layers 102, 104 and the thickness of each layer 102, 104 are determined from the spectral attributes acquired from a spectroscopic analysis of a characteristic of the material of interest using a conventional spectroscopic instrument. The spectrum of interest of a given characteristic of interest typically includes any number of different wavelengths. It should be understood that the exemplary ICE 100 in FIG. 1 does not in fact represent any particular characteristic of a given material of interest, but is provided for purposes of illustration only. Consequently, the number of layers 102, 104 and their relative thicknesses, as shown in FIG. 1, bear no correlation to any particular characteristic of a given material of interest. Nor are the layers 102, 104 and their relative thicknesses necessarily drawn to scale, and therefore should not be considered limiting of the present disclosure. Moreover, those skilled in the art will readily recognize that the materials that make up each layer 102, 104 (e.g., Si and SiO₂) may vary, depending on the application, cost of materials, and/or applicability of the material to the given material of interest.

In some embodiments, the material of each layer 102, 104 can be doped or two or more materials can be combined in a manner to achieve the desired optical characteristic. In addition to solids, the exemplary ICE 100 may also contain liquids and/or gases, optionally in combination with solids, in order to produce a desired optical characteristic. In the case of gases and liquids, the ICE 100 can contain a corresponding vessel (not shown), which houses the gases or liquids. Exemplary variations of the ICE 100 may also include holographic optical elements, gratings, piezoelectric, light pipe, digital light pipe (DLP), variable optical attenuators, and/or acousto-optic elements, for example, that can create transmission, reflection, and/or absorptive properties of interest.

The multiple layers 102, 104 exhibit different refractive indices. By properly selecting the materials of the layers 102, 104 and their relative thickness and spacing, the ICE 100 may be configured to selectively pass/reflect/refract predetermined fractions of electromagnetic radiation at different wavelengths. Each wavelength is given a predetermined weighting or loading factor. The thickness and spacing of the layers 102, 104 may be determined using a variety of approximation methods from the spectrograph of the characteristic of interest. These methods may include inverse Fourier transform (IFT) of the optical transmission spectrum and structuring the ICE 100 as the physical representation of the IFT. The approximations convert the IFT into a structure based on known materials with constant refractive indices. Further information regarding the structures and design of exemplary integrated computational elements (also referred to as multivariate optical elements) is provided in Applied Optics, Vol. 35, pp. 5484-5492 (1996) and Vol. 129, pp. 2876-2893, which is hereby incorporated by reference.

The weightings that the layers 102, 104 of the ICE 100 apply at each wavelength are set to the regression weightings described with respect to a known equation, or data, or spectral signature. Briefly, the ICE 100 may be configured to perform the dot product of the input light beam into the ICE 100 and a desired loaded regression vector represented by each layer 102, 104 for each wavelength. As a result, the output light intensity of the ICE 100 is related to the characteristic of interest. Further details regarding how the exemplary ICE 100 is able to distinguish and process electromagnetic radiation related to the characteristic of interest are described in U.S. Pat. No. 6,198,531 entitled “Optical Computational System;” U.S. Pat. No. 6,529,276 entitled “Optical Computational System;” and U.S. Pat. No. 7,920,258 entitled “Optical Analysis System and Elements to Isolate Spectral Region;” previously incorporated herein by reference.

Referring now to FIG. 2, illustrated is a block diagram that non-mechanistically illustrates how an optical computing device 200 is able to distinguish electromagnetic radiation related to a characteristic of interest from other electromagnetic radiation. As shown in FIG. 2, after being illuminated with incident electromagnetic radiation, a material of interest 202 (e.g., a cement sheath, a displacement composition, or an analyte thereof) produces an output of electromagnetic radiation (e.g., sample-interacted light), some of which is electromagnetic radiation 204 corresponding to the characteristic of interest and some of which is background electromagnetic radiation 206 corresponding to other characteristics of the material of interest 202.

Although not specifically shown, one or more spectral elements may be employed in the device 200 in order to restrict the optical wavelengths and/or bandwidths of the system and thereby eliminate unwanted electromagnetic radiation existing in wavelength regions that have no importance. Such spectral elements can be located anywhere along the optical train, but are typically employed directly after the light source, which provides the initial electromagnetic radiation. Various configurations and applications of spectral elements in optical computing devices may be found in commonly owned U.S. Pat. No. 6,198,531 entitled “Optical Computational System;” U.S. Pat. No. 6,529,276 entitled “Optical Computational System;” U.S. Pat. No. 7,123,844 entitled “Optical Computational System;” U.S. Pat. No. 7,834,999 “Optical Analysis System and Optical Train;” U.S. Pat. No. 7,911,605 entitled “Multivariate Optical Elements for Optical Analysis System;” U.S. Pat. No. 7,920,258 entitled “Optical Analysis System and Elements to Isolate Spectral Region;” and U.S. Pat. No. 8,049,881 entitled “Optical Analysis System and Methods for Operating Multivariate Optical Elements in a Normal Incidence Orientation;” and U.S. patent application Ser. No. 12/094,460 entitled “Methods of High-Speed Monitoring Based on the Use of Multivariate Optical Elements;” Ser. No. 12/094,465 entitled “Optical Analysis System for Dynamic Real-Time Detection and Measurement;” and Ser. No. 13/456,467 entitled “Imaging Systems for Optical Computing Devices;” incorporated herein by reference, as indicated above.

The beams of electromagnetic radiation 204,206 impinge upon the optical computing device 200, which contains an exemplary ICE 208 therein. In the illustrated embodiment, the ICE 208 may be configured to produce optically interacted light, for example, transmitted optically interacted light 210 and reflected optically interacted light 214. In operation, the ICE 208 may be configured to distinguish the electromagnetic radiation 204 from the background electromagnetic radiation 206.

The transmitted optically interacted light 210, which may be related to the characteristic of interest of the material of interest 202, may be conveyed to a detector 212 for analysis and quantification. In some embodiments, the detector 212 is configured to produce an output signal in the form of a voltage that corresponds to the particular characteristic of the material of interest 202. In at least one embodiment, the signal produced by the detector 212 and the characteristic of a material of interest 202 (e.g., the concentration of an analyte, pH, porosity, or the like) may be directly proportional. In other embodiments, the relationship may be a polynomial function, an exponential function, and/or a logarithmic function. The reflected optically interacted light 214, which may be related to other characteristics of the material of interest 202, can be directed away from detector 212. In alternative configurations, the ICE 208 may be configured such that the reflected optically interacted light 214 can be related to the characteristic of interest, and the transmitted optically interacted light 210 can be related to other characteristics in the material of interest 202.

In some embodiments, a second detector 216 can be present and arranged to detect the reflected optically interacted light 214. In other embodiments, the second detector 216 may be arranged to detect the electromagnetic radiation 204,206 derived from the material of interest 202 or electromagnetic radiation directed toward or before the material of interest 202. Without limitation, the second detector 216 may be used to detect radiating deviations stemming from an electromagnetic radiation source (not shown), which provides the electromagnetic radiation (i.e., light) to the device 200. For example, radiating deviations can include, but are not limited to, intensity fluctuations in the electromagnetic radiation, interferent fluctuations (e.g., dust or other interferents passing in front of the electromagnetic radiation source), coatings on windows included with the optical computing device 200, combinations thereof, or the like. In some embodiments, a beam splitter (not shown) can be employed to split the electromagnetic radiation 204,206, and the transmitted or reflected electromagnetic radiation can then be directed to one or more ICE 208. That is, in such embodiments, the ICE 208 does not function as a type of beam splitter, as depicted in FIG. 2, and the transmitted or reflected electromagnetic radiation simply passes through the ICE 208, being computationally processed therein, before travelling to the detector 212.

The characteristic(s) of the material of interest 202 being analyzed using the optical computing device 200 can be further processed and/or analyzed computationally to provide additional information regarding the properties of the material of interest 202. In some embodiments, the characteristic of the material of interest 202 can be used to analyze for microannulus indicators.

In some embodiments, the characteristics of the material of interest determined using the optical computing devices 200 can be associated with a timestamp. A timestamp may be useful in reviewing and analyzing the history of the characteristic of interest, which may be of added value in determining if a microannulus has formed. In some embodiments, the characteristics, optionally timestamped, of the material of interest determined using the optical computing devices 200 can be fed into an algorithm operating under computer control. The algorithm may be configured to make predictions on the presence, formation timeline, and/or extent of a microannulus. In some embodiments, the algorithm can produce an output that is readable by an operator who can manually take appropriate action, like initiation of a remedial operation, if needed, based upon the output.

The algorithm can be part of an artificial neural network configured to use each detected characteristic of interest in order to evaluate the overall property(s) of the material of interest 202 and determine if a microannulus has formed, and in some embodiments, the extent of microannulus formation. Illustrative but non-limiting artificial neural networks are described in commonly owned U.S. patent application Ser. No. 11/986,763 entitled “Determining Stimulation Design Parameters Using Artificial Neural Networks Optimized with a Genetic Algorithm,” which is incorporated herein by reference. It is to be recognized that an artificial neural network can be trained using samples of substances having known characteristics, and thereby generating a virtual library. As the virtual library available to the artificial neural network becomes larger, the neural network can become more capable of accurately determining microannulus formation, and optionally the extent of microannulus formation.

It is recognized that the various embodiments herein directed to computer control and artificial neural networks, including various blocks, modules, elements, components, methods, and algorithms, can be implemented using computer hardware, software, combinations thereof, and the like. To illustrate this interchangeability of hardware and software, various illustrative blocks, modules, elements, components, methods, and algorithms have been described generally in terms of their functionality. Whether such functionality is implemented as hardware or software will depend upon the particular application and any imposed design constraints. For at least this reason, it is to be recognized that one of ordinary skill in the art can implement the described functionality in a variety of ways for a particular application. Further, various components and blocks can be arranged in a different order or partitioned differently, for example, without departing from the scope of the embodiments expressly described.

Computer hardware used to implement the various illustrative blocks, modules, elements, components, methods, and algorithms described herein can include a processor configured to execute one or more sequences of instructions, programming stances, or code stored on a non-transitory, computer-readable medium. The processor can be, for example, a general purpose microprocessor, a microcontroller, a digital signal processor, an application specific integrated circuit, a field programmable gate array, a programmable logic device, a controller, a state machine, a gated logic, discrete hardware components, an artificial neural network, or any like suitable entity that can perform calculations or other manipulations of data. In some embodiments, computer hardware can further include elements, for example, a memory (e.g., random access memory (RAM), flash memory, read only memory (ROM), programmable read only memory (PROM), erasable read only memory (EPROM)), registers, hard disks, removable disks, CD-ROMS, DVDs, or any other like suitable storage device or medium.

Executable sequences described herein can be implemented with one or more sequences of code contained in a memory. In some embodiments, such code can be read into the memory from another machine-readable medium. Execution of the sequences of instructions contained in the memory can cause a processor to perform the process steps described herein. One or more processors in a multi-processing arrangement can also be employed to execute instruction sequences in the memory. In addition, hard-wired circuitry can be used in place of or in combination with software instructions to implement various embodiments described herein. Thus, the present embodiments are not limited to any specific combination of hardware and/or software.

As used herein, a machine-readable medium will refer to any medium that directly or indirectly provides instructions to a processor for execution. A machine-readable medium can take on many forms including, for example, non-volatile media, volatile media, and transmission media. Non-volatile media can include, for example, optical and magnetic disks. Volatile media can include, for example, dynamic memory. Transmission media can include, for example, coaxial cables, wire, fiber optics, and wires that form a bus. Common forms of machine-readable media can include, for example, floppy disks, flexible disks, hard disks, magnetic tapes, other like magnetic media, CD-ROMs, DVDs, other like optical media, punch cards, paper tapes and like physical media with patterned holes, RAM, ROM, PROM, EPROM, and flash EPROM.

In some embodiments, the data collected, and optionally analyzed, using the optical computing devices described herein can be transmitted from the analysis point within the wellbore to the surface in real-time or near real-time. Transmitting data real-time or near real-time may be undertaken using wired means (e.g., fiber optics) or wireless means (e.g., telemetry).

In some embodiments, the data collected, and optionally analyzed, using the optical computing devices described herein can be stored in, for example, an on-board memory or the like, and then subsequently downloaded to an external processing device for consideration. Downloading data may be transmitted by wired means (e.g., fiber optics) or wireless means (e.g., telemetry). In some embodiments, downloading may be achieved by running a tool through at least a portion of the wellbore such that the tool wirelessly downloads the data to an external processing device.

In some embodiments, the data collected, and optionally analyzed, can be communicated (wired or wirelessly) to a remote location by a communication system (e.g., satellite communication or wide area network communication) for further analysis. The communication system can also allow remote monitoring and operation of a process to take place. Automated control with a long-range communication system can further facilitate the performance of remote job operations. In particular, an artificial neural network can be used in some embodiments to facilitate the performance of remote job operations (e.g., remedial operations to repair a microannulus). That is, remote job operations can be conducted automatically in some embodiments. In other embodiments, however, remote job operations can occur under direct operator control, where the operator is not at the job site.

In some embodiments, the data collected using the optical computing devices can be archived along with data associated with operational parameters being logged at a job site. Evaluation of job performance can then be assessed and improved for future operations or such information can be used to design subsequent operations.

Referring now to FIG. 3A, illustrated is an exemplary system 300 for monitoring a material of interest (e.g., a cement sheath 302 and/or a displacement composition 350) for an indicator of a microannulus 352 having formed, according to one or more embodiments. In the illustrated embodiment, the cement sheath 302 may be disposed about and in contact with an exterior surface 340 of a casing 304. While FIG. 3A is depicted as a vertical wellbore, it should be appreciated that the wellbore may be arranged substantially vertical, substantially horizontal, or any directional configuration therebetween, without departing from the scope of the disclosure. The system 300 may include at least one optical computing device 306, which may be similar in some respects to the optical computing device 200 of FIG. 2, and therefore may be best understood with reference thereto.

Referring now to FIG. 3B, with continued reference to FIG. 3A, the optical computing device 306 may be housed within a housing 342 configured to substantially protect the internal components of the optical computing device 306 from damage or contamination from the external environment. In some embodiments, the housing may operate to mechanically couple the device 306 to the casing 304 with, for example, mechanical fasteners, brazing or welding techniques, adhesives, magnets, combinations thereof or the like. In operation, the housing 342 may be designed to withstand the pressures that may be experienced within or outside the casing 304 and thereby provide a fluid tight seal against external contamination. As described in greater detail below, the optical computing device 306 may be useful in determining a characteristic of the material of interest (e.g., the cement sheath 302 and/or a displacement composition 350).

By way of nonlimiting example, because some chemicals may deteriorate a cement composition, monitoring the cement sheath 302 for the characteristic of porosity may help determine if a microannulus 352 has formed and provide an opportunity to repair the cement sheath 302 with a remedial operation.

By way of another nonlimiting example, the optical computing device 306 may be configured to measure a characteristic of an oleaginous fluid, an example of the displacement composition 350. As such, after formation and setting of the casing 304, the optical computing device 306 may collect data indicating that the oleaginous fluid is not present. Then, after some time has passed, the optical computing device 306 may return a positive measurement for the characteristic of the oleaginous fluid, thereby indicating the possible formation of the microannulus 352. The optical computing device 306 may be configured to inform the user (either wired or wirelessly) of the positive measurement. After the user has been alerted to the positive measurement, appropriate corrective action (e.g., a remedial operation) may be taken, if appropriate. Further, in some embodiments, the optical computing device 306 may be used after the appropriate corrective action so as to determine the efficacy of such action. For example, the optical computing device 306 may again be configured to collect data indicating that the oleaginous fluid is not present.

In some embodiments, the device 306 may include an electromagnetic radiation source 308 configured to emit or otherwise generate electromagnetic radiation 310. The electromagnetic radiation source 308 may be any device capable of emitting or generating electromagnetic radiation, as defined herein. For example, the electromagnetic radiation source 308 may be a light bulb, a light emitting device (LED), a laser, a blackbody, a photonic crystal, an X-Ray source, combinations thereof, or the like. In some embodiments, a lens 312 may be configured to collect or otherwise receive the electromagnetic radiation 310 and direct a beam 314 of electromagnetic radiation 310 toward the material of interest (e.g., the cement sheath 302 and/or the displacement composition 350). The lens 312 may be any type of optical device configured to transmit or otherwise convey the electromagnetic radiation 310 as desired. For example, the lens 312 may be a normal lens, a Fresnel lens, a diffractive optical element, a holographic graphical element, a mirror (e.g., a focusing mirror), a type of collimator, or any other electromagnetic radiation transmitting device known to those skilled in art. In other embodiments, the lens 312 may be omitted from the device 306 and the electromagnetic radiation 310 may instead be directed toward the material of interest (e.g., the cement sheath 302 and/or the displacement composition 350) directly from the electromagnetic radiation source 308.

In one or more embodiments, the device 306 may also include a sampling window 316 arranged adjacent to or otherwise in contact with the material of interest (e.g., the cement sheath 302 and/or the displacement composition 350) for detection purposes. The sampling window 316 may be made from a variety of transparent, rigid or semi-rigid materials that are configured to allow transmission of the electromagnetic radiation 310 therethrough. For example, the sampling window 316 may be made of, but is not limited to, glasses, plastics, semi-conductors, crystalline materials, polycrystalline materials, hot or cold-pressed powders, combinations thereof, or the like. In order to remove ghosting or other imaging issues resulting from reflectance on the sampling window 316, the system 300 may employ one or more internal reflectance elements (“IRE”), such as those described in co-owned U.S. Pat. No. 7,697,141 entitled “In Situ Optical Computational Fluid Analysis System and Method,” and/or one or more imaging systems, such as those described in co-owned U.S. patent application Ser. No. 13/456,467 entitled “Imaging Systems for Optical Computing Devices,” the contents of each hereby being incorporated by reference.

After passing through the sampling window 316, the electromagnetic radiation 310 impinges upon and optically interacts with the material of interest (e.g., the cement sheath 302 and/or the displacement composition 350). As a result, optically interacted radiation 318 is generated by and reflected from the material of interest (e.g., the cement sheath 302 and/or the displacement composition 350). Those skilled in the art, however, will readily recognize that alternative variations of the device 306 may allow the optically interacted radiation 318 to be generated by being transmitted, scattered, diffracted, absorbed, emitted, or re-radiated by and/or from the material of interest (e.g., the cement sheath 302 and/or the displacement composition 350), without departing from the scope of the disclosure.

The optically interacted radiation 318 generated by the interaction with the material of interest (e.g., the cement sheath 302 and/or the displacement composition 350) may be directed to or otherwise be received by an ICE 320 arranged within the device 306. The ICE 320 may be a spectral component substantially similar to the ICE 100 described above with reference to FIG. 1. Accordingly, in operation the ICE 320 may be configured to receive the optically interacted radiation 318 and produce modified electromagnetic radiation 322 corresponding to a particular characteristic of the material of interest (e.g., the cement sheath 302 and/or the displacement composition 350). In particular, the modified electromagnetic radiation 322 is electromagnetic radiation that has optically interacted with the ICE 320, whereby an approximate mimicking of the regression vector corresponding to the characteristic of the material of interest (e.g., the cement sheath 302 and/or the displacement composition 350) is obtained.

It should be noted that, while FIG. 3B depicts the ICE 320 as receiving reflected electromagnetic radiation from the material of interest (e.g., the cement sheath 302 and/or the displacement composition 350), the ICE 320 may be arranged at any point along the optical train of the device 306, without departing from the scope of the disclosure. For example, in one or more embodiments, the ICE 320 (as shown in dashed) may be arranged within the optical train prior to the sampling window 316 and equally obtain substantially the same results. In other embodiments, the sampling window 316 may serve a dual purpose as both a transmission window and the ICE 320 (i.e., a spectral components). In yet other embodiments, the ICE 320 may generate the modified electromagnetic radiation 322 through reflection, instead of transmission therethrough.

Moreover, while only one ICE 320 is shown in the device 306, embodiments are contemplated herein which include the use of at least two ICE components in the device 306 configured to cooperatively determine the characteristic of the material of interest (e.g., the cement sheath 302 and/or the displacement composition 350). For example, two or more ICE components may be arranged in series or parallel within the device 306 and configured to receive the optically interacted radiation 318 and thereby enhance sensitivities and detector limits of the device 306. In other embodiments, two or more ICE may be arranged on a movable assembly, such as a rotating disc or an oscillating linear array, which moves such that the individual ICE components are able to be exposed to or otherwise optically interact with electromagnetic radiation for a distinct brief period of time. The two or more ICE components in any of these embodiments may be configured to be either associated or disassociated with the characteristic of the material of interest (e.g., the cement sheath 302 and/or the displacement composition 350). In other embodiments, the two or more ICE may be configured to be positively or negatively correlated with the characteristic of the material of interest (e.g., the cement sheath 302 and/or the displacement composition 350). These optional embodiments employing two or more ICE components are further described in co-pending U.S. patent application Ser. No. 13/456,264 entitled “Methods and Devices for Optically Determining a Characteristic of a Substance,” Ser. No. 13/456,405 entitled “Methods and Devices for Optically Determining A Characteristic of a Substance,” Ser. No. 13/456,302 entitled “Methods and Devices for Optically Determining A Characteristic of a Substance,” and Ser. No. 13/456,327 entitled “Methods and Devices for Optically Determining A Characteristic of a Substance,” the contents of which are hereby incorporated by reference in their entireties.

In some embodiments, it may be desirable to monitor more than one characteristic of interest at a time using the device 306. In such embodiments, various configurations for multiple ICE components can be used, where each ICE component is configured to detect a particular and/or distinct characteristic of interest. In some embodiments, the characteristic can be analyzed sequentially using multiple ICE components that are provided a single beam of electromagnetic radiation being reflected from or transmitted through the material of interest (e.g., the cement sheath 302 and/or the displacement composition 350). In some embodiments, as briefly mentioned above, multiple ICE components can be arranged on a rotating disc, where the individual ICE components are only exposed to the beam of electromagnetic radiation for a short time. Advantages of this approach can include the ability to analyze multiple characteristics of the material of interest (e.g., the cement sheath 302 and/or the displacement composition 350) using a single optical computing device and the opportunity to assay additional characteristics of interest simply by adding additional ICE components to the rotating disc. In various embodiments, the rotating disc can be turned at a frequency of about 10 RPM to about 30,000 RPM such that each characteristic of the material of interest (e.g., the cement sheath 302 and/or the displacement composition 350) is measured rapidly. In some embodiments, these values can be averaged over an appropriate time domain (e.g., about 1 millisecond to about 1 hour) to more accurately determine the characteristic of the material of interest (e.g., the cement sheath 302 and/or the displacement composition 350).

In other embodiments, multiple optical computing devices can be placed in at least one location along the casing 304, where each optical computing device contains a unique ICE component that is configured to detect a particular characteristic of the material of interest (e.g., the cement sheath 302 and/or the displacement composition 350). In such embodiments, a beam splitter can divert a portion of the electromagnetic radiation being reflected by or emitted from the material of interest (e.g., the cement sheath 302 and/or the displacement composition 350) and into each optical computing device. Each optical computing device, in turn, can be coupled to a corresponding detector or detector array that is configured to detect and analyze an output of electromagnetic radiation from the respective optical computing device. Parallel configurations of optical computing devices can be particularly beneficial for applications that require low power inputs and/or no moving parts, e.g., long-term monitoring of the health of the cement sheath.

Those skilled in the art will appreciate that any of the foregoing configurations can further be used in combination with a series configuration in any of the present embodiments. For example, two optical computing devices having a rotating disc with a plurality of ICE components arranged thereon can be placed in series for performing an analysis at a single location along the length of the casing 304. Likewise, multiple detection stations, each containing optical computing devices in parallel, can be placed in series for performing a similar analysis.

With continued reference to FIG. 3B, the modified electromagnetic radiation 322 generated by the ICE 320 may subsequently be conveyed to a detector 324 for quantification of the signal. The detector 324 may be any device capable of detecting electromagnetic radiation, and may be generally characterized as an optical transducer. In some embodiments, the detector 324 may be, but is not limited to, a thermal detector such as a thermopile or photoacoustic detector, a semiconductor detector, a piezo-electric detector, a charge coupled device (CCD) detector, a video or array detector, a split detector, a photon detector (e.g., a photomultiplier tube), photodiodes, combinations thereof, or the like, or other detectors known to those skilled in the art.

In some embodiments, the detector 324 may be configured to produce an output signal 326 in real-time or near real-time in the form of a voltage (or current) that corresponds to the particular characteristic of the material of interest (e.g., the cement sheath 302 and/or the displacement composition 350). The voltage returned by the detector 324 is essentially the dot product of the optical interaction of the optically interacted radiation 318 with the respective ICE 320 as a function of a characteristic the material of interest (e.g., the cement sheath 302 and/or the displacement composition 350). As such, the output signal 326 produced by the detector 324 and the characteristic of the material of interest (e.g., the cement sheath 302 and/or the displacement composition 350) may be related, for example, directly proportional. In other embodiments, however, the relationship may correspond to a polynomial function, an exponential function, a logarithmic function, and/or a combination thereof.

In some embodiments, the device 306 may include a second detector 328, which may be similar to the first detector 324 in that it may be any device capable of detecting electromagnetic radiation. Similar to the second detector 216 of FIG. 2, the second detector 328 of FIG. 3B may be used to detect radiating deviations stemming from the electromagnetic radiation source 308. Undesirable radiating deviations can occur in the intensity of the electromagnetic radiation 310 due to a wide variety of reasons and potentially causing various negative effects on the device 306. These negative effects can be particularly detrimental for measurements taken over a period of time. In some embodiments, radiating deviations can occur as a result of a build-up of film or material on the sampling window 316 which has the effect of reducing the amount and quality of light ultimately reaching the first detector 324. Without proper compensation, such radiating deviations could result in false readings and the output signal 326 would no longer be primarily or accurately related to the characteristic of interest.

To compensate for these types of undesirable effects, the second detector 328 may be configured to generate a compensating signal 330 generally indicative of the radiating deviations of the electromagnetic radiation source 308, and thereby normalize the output signal 326 generated by the first detector 324. As illustrated, the second detector 328 may be configured to receive a portion of the optically interacted radiation 318 via a beamsplitter 332 in order to detect the radiating deviations. In other embodiments, however, the second detector 328 may be arranged to receive electromagnetic radiation from any portion of the optical train in the device 306 in order to detect the radiating deviations, without departing from the scope of the disclosure.

In some applications, the output signal 326 and the compensating signal 330 may be conveyed to or otherwise received by a signal processor 334 communicably coupled to both the detectors 320,328. The signal processor 334 may be a computer including a non-transitory machine-readable medium, and may be configured to computationally combine the compensating signal 330 with the output signal 326 in order to normalize the output signal 326 in view of any radiating deviations detected by the second detector 328. In some embodiments, computationally combining the output and compensating signals 326,330 may entail computing a ratio of the two signals 326,330. For example, the characteristic of a material of interest or the magnitude of each characteristic determined using the optical computing device 306 can be fed into an algorithm run by the signal processor 334.

In real-time or near real-time, the signal processor 334 may be configured to provide a resulting output signal 336 corresponding to a characteristic of the material of interest (e.g., the cement sheath 302 and/or the displacement composition 350). The resulting output signal 336 may be readable by an operator who can consider the results and make proper adjustments or take appropriate action, if needed, based upon the measured characteristic of the material of interest (e.g., the cement sheath 302 and/or the displacement composition 350). In some embodiments, the resulting signal output 328 may be conveyed, either wired or wirelessly, to the user for consideration. In other embodiments, the resulting output signal 336 may be recognized by the signal processor 334 as being within or without a predetermined or preprogrammed range that indicates the possible formation of the microannulus 352. If the resulting output signal 336 exceeds the predetermined or preprogrammed range of operation, the signal processor 334 may be configured to alert the user of a potential formation of the microannulus 352 so appropriate corrective action (e.g., a remedial operation) may be taken.

By way of nonlimiting example, in some embodiments, the device 306 may be configured to measure water concentration. As water is present, to some degree, in cement compositions, a threshold water concentration may be set at a level similar to that of a set cement compositions. However, when the microannulus 352 forms and is infiltrated by a displacement composition 350 that comprises water, the device 306 may detect water above the threshold concentration and alter a user to the potential formation of the microannulus 352.

Referring now to FIG. 4, illustrated is an exemplary system 400 for monitoring a fluid according to one or more embodiments. In the illustrated embodiment, the system 400 includes a plurality of optical computing devices 406,406′,406″ coupled to a casing 404 in series along the length of the casing 404. Each optical computing device 406,406′,406″ may be similar to the optical computing device 306 of FIGS. 3A and 3B, and therefore will not be described again in detail. Such a plurality of optical computing devices 406,406′,406″ may be advantageous to monitor multiple locations along a casing for microannulus formation. As with the embodiments discussed above, the plurality of optical computing devices 406,406′,406″ may independently include multiple ICE components and be configured to measure one or more characteristics of interest and analyzed for indicators of microannulus formation.

In some embodiments, each of the plurality of optical computing devices 406,406′,406″ may be designed to analyze the same or different characteristics of interest. For example, optical computing device 406 can be configured to measure a concentration of an analyte (or plurality of analytes) found in formation fluids where an increase in concentration may indicate formation fluid infiltration and indicate microannulus formation; optical computing device 406′ can be configured to analyze for a characteristic of the cement sheath 402 where a decrease in signal could indicate microannulus formation (e.g., because of pull-away from the device and/or infiltration of a displacement composition between the cement sheath 402 and the optical computing device 406′); and optical computing device 406″ can be configured to measure a concentration of an analyte (or plurality of analytes) found in a wellbore fluid (e.g., a concentration of an analyte like a tracer or probe analyte) where an increase in concentration may indicate wellbore fluid infiltration and indicate microannulus formation.

Those skilled in the art will readily appreciate the various and numerous applications that the systems 300 and 400, and alternative configurations thereof, may be suitably used with. For example, some embodiments of the present disclosure may involve measuring at least one characteristic of interest of a cement sheath with the optical computing devices generally disclosed herein. In other embodiments, the optical computing devices may be configured to measure or otherwise monitor the presence or absence of a displacement composition (e.g., a formation fluid or a wellbore fluid) which may interpose the outer circumferential surface of a casing and the cement sheath. As generally described above, the detection of a displacement composition may indicate the formation of a microannulus between the outer circumferential surface of a casing and the cement sheath. To achieve such detection, the optical computing devices may be disposed in any suitable location including, but not limited to, relative to an exterior surface of a casing, relative to an exterior surface of a collar, relative to a centralizer, or relative to an exterior surface of a casing shoe.

In some embodiments, when a microannulus indicated by the methods and/or systems described herein, one or more remedial operations (e.g., squeeze operations) to reverse the effects of the microannulus may be initiated. In some embodiments, the optical computing device may be used to analyze for efficacy of the remediation operation, e.g., a change in output signal that indicates cement has been properly placed in the microannulus. For example, optical computing devices configured to measure a characteristic of the cement sheath may have a signal decrease when the cement sheath pulls away from the casing. Then, after a remedial operation where cement is placed in the microannulus, the output signal may increase. In another example, optical computing devices configured to measure a characteristic of a displacement composition may have a signal increase when the displacement composition infiltrates between the cement sheath and the casing. Then, after a remedial operation where cement is placed in the microannulus, the output signal may decrease.

It should also be noted that the various drawings provided herein are not necessarily drawn to scale nor are they, strictly speaking, depicted as optically correct as understood by those skilled in optics. Instead, the drawings are merely illustrative in nature and used generally herein in order to supplement understanding of the systems and methods provided herein. Indeed, while the drawings may not be optically accurate, the conceptual interpretations depicted therein accurately reflect the exemplary nature of the various embodiments disclosed.

Therefore, the present invention is well adapted to attain the ends and advantages mentioned as well as those that are inherent therein. The particular embodiments disclosed above are illustrative only, as the present invention may be modified and practiced in different but equivalent manners apparent to those skilled in the art having the benefit of the teachings herein. Furthermore, no limitations are intended to the details of construction or design herein shown, other than as described in the claims below. It is therefore evident that the particular illustrative embodiments disclosed above may be altered, combined, or modified and all such variations are considered within the scope and spirit of the present invention. The invention illustratively disclosed herein suitably may be practiced in the absence of any element that is not specifically disclosed herein and/or any optional element disclosed herein. While compositions and methods are described in terms of “comprising,” “containing,” or “including” various components or steps, the compositions and methods can also “consist essentially of” or “consist of” the various components and steps. All numbers and ranges disclosed above may vary by some amount. Whenever a numerical range with a lower limit and an upper limit is disclosed, any number and any included range falling within the range is specifically disclosed. In particular, every range of values (of the form, “from about a to about b,” or, equivalently, “from approximately a to b,” or, equivalently, “from approximately a-b”) disclosed herein is to be understood to set forth every number and range encompassed within the broader range of values. Also, the terms in the claims have their plain, ordinary meaning unless otherwise explicitly and clearly defined by the patentee. Moreover, the indefinite articles “a” or “an,” as used in the claims, are defined herein to mean one or more than one of the element that it introduces. If there is any conflict in the usages of a word or term in this specification and one or more patent or other documents that may be incorporated herein by reference, the definitions that are consistent with this specification should be adopted. 

The invention claimed is:
 1. A system comprising: a cement sheath disposed about and in contact with at least a portion of an exterior surface of a casing; and at least one optical computing device arranged on the casing, the at least one optical computing device having at least one integrated computational element configured to optically interact with a material of interest and thereby generate optically interacted light, and at least one detector arranged to receive the optically interacted light and generate an output signal corresponding to a characteristic of the material of interest, the material of interest comprising at least one selected from the group consisting of the cement sheath, a displacement composition disposed between the cement sheath and the exterior surface of the casing, and any combination thereof.
 2. The system of claim 1 further comprising: a signal processor communicably coupled to the at least one detector for receiving the output signal, the signal processor being configured to determine the characteristic of the material of interest.
 3. The system of claim 1, wherein the at least one detector is a first detector and the system further comprises a second detector arranged to detect electromagnetic radiation from the electromagnetic radiation source and thereby generate a compensating signal indicative of electromagnetic radiating deviations.
 4. The system of claim 1, wherein the characteristic of the material of interest is at least one selected from the group consisting of chemical composition, impurity content, pH, viscosity, density, ionic strength, total dissolved solids, salt content, porosity, opacity, bacteria content, particle size distribution, color, temperature, hydration level, and an analyte oxidation state.
 5. The system of claim 1, wherein the characteristic of the material of interest is a characteristic of a analytes of the material of interest, the analyte comprising at least one selected from the group consisting of water, salt, a mineral, wollastonite, metakaolin, pumice, a cement, Portland cement, gypsum cement, a calcium phosphate cement, a high alumina content cement, a silica cement, a high alkalinity cement, a filler, fly ash, fume silica, hydrated lime, pozzolanic material, sand, barite, calcium carbonate, ground marble, iron oxide, manganese oxide, glass bead, crushed glass, a crushed drill cutting, ground vehicle tire, crushed rock, ground asphalt, crushed concrete, crushed cement, ilmenite, hematite, silica flour, fume silica, fly ash, an elastomer, a polymer, diatomaceous earth, a highly swellable clay mineral, nitrogen, air, a fiber, natural rubber, acrylate butadiene rubber, polyacrylate rubber, isoprene rubber, chloroprene rubber, butyl rubber, brominated butyl rubber, chlorinated butyl rubber, chlorinated polyethylene, neoprene rubber, styrene butadiene copolymer rubber, sulphonated polyethylene, ethylene acrylate rubber, epichlorohydrin ethylene oxide copolymer, ethylene propylene rubber, ethylene propylene diene terpolymer rubber, ethylene vinyl acetate copolymer, fluorosilicone rubber, silicone rubber, poly-2,2,1-bicycloheptene, alkylstyrene, crosslinked substituted vinyl acrylate copolymer, nitrile rubber, hydrogenated nitrile rubber, fluoro rubber, perfluoro rubber, tetrafluoroethylene/propylene, starch polyacrylate acid graft copolymer, polyvinyl alcohol cyclic acid anhydride graft copolymer, isobutylene maleic anhydride, acrylic acid type polymer, vinylacetate-acrylate copolymer, polyethylene oxide polymer, carboxymethyl cellulose polymer, starch-polyacrylonitrile graft copolymer, polymethacrylate, polyacrylamide, and non-soluble acrylic polymer), hydrocarbon, an acid, an acid-generating compound, a base, a base-generating compound, a biocide, a surfactant, a scale inhibitor, a corrosion inhibitor, a gelling agent, a crosslinking agent, an anti-sludging agent, a foaming agent, a defoaming agent, an antifoam agent, a emulsifying agent, a de-emulsifying agent, a iron control agent, a proppants or other particulate, a gravel, particulate diverter, a salt, a cement slurry loss control additive, a gas migration control additive, a gas, air, nitrogen, carbon dioxide, hydrogen sulfide, argon, helium, a hydrocarbon gas, methane, ethane, butane, catalyst, a clay control agent, a chelating agent, a corrosion inhibitor, a dispersant, a flocculant, a scavenger, an H₂S scavenger, a CO₂ scavenger, an O₂ scavenger, a lubricant, a breaker, a delayed release breaker, a friction reducer, a bridging agent, a viscosifier, a weighting agent, a solubilizer, a rheology control agent, a viscosity modifier, a pH control agent, a buffer, a hydrate inhibitor, a relative permeability modifier, a diverting agent, a consolidating agent, a fibrous material, a bactericide, a tracer, a probe, a nanoparticle, a paraffin wax, an asphaltene, a foam, sand, and any combination thereof.
 6. The system of claim 1, wherein the characteristic of the material of interest is related to an indicator of microannulus formation.
 7. The system of claim 6, wherein the indicator of microannulus formation comprises at least one selected from the group consisting of presence of the displacement composition, porosity changes of the cement sheath, temperature changes of the material of interest, pH level of the material of interest, decreased output signal relating to the characteristic of the material of interest, changes to a chemical composition of the cement sheath, and any combination thereof.
 8. A system comprising: a cement sheath disposed about and in contact with at least a portion of an exterior surface of a casing; and at least one integrated computational element configured to optically interact with a material of interest and thereby generate optically interacted light, and at least one detector arranged to receive the optically interacted light and generate an output signal corresponding to a characteristic of the material of interest, the material of interest comprising at least one selected from the group consisting of the cement sheath, a displacement composition disposed between the cement sheath and the exterior surface of the casing, and any combination thereof.
 9. The system of claim 8, wherein the at least one integrated computational element is operably coupled to at least one selected from the group consisting of the casing, a centralizer operably coupled to the casing, a casing shoe operably coupled to the casing, and a collar operably coupled to the casing.
 10. A method comprising: optically interacting a material of interest and at least one integrated computational element, thereby generating an output signal corresponding to a characteristic of the material of interest, the material of interest comprising at least one selected from the group consisting of a cement sheath disposed about and in contact with at least a portion of an exterior surface of a casing, a displacement composition disposed between the cement sheath and the exterior surface of the casing, and any combination thereof.
 11. The method of claim 10, wherein the characteristic of the material of interest is at least one selected from the group consisting of chemical composition, impurity content, pH, viscosity, density, ionic strength, total dissolved solids, salt content, porosity, opacity, bacteria content, particle size distribution, color, temperature, hydration level, and an analyte oxidation state.
 12. The method of claim 10, wherein the characteristic of the material of interest is related to an indicator of microannulus formation.
 13. The method of claim 12, wherein the indicator of microannulus formation comprises at least one selected from the group consisting of presence of the displacement composition, porosity changes of the cement sheath, temperature changes of the material of interest, pH level of the material of interest, decreased output signal relating to the characteristic of the material of interest, changes to a chemical composition of the cement sheath, and any combination thereof.
 14. The method of claim 10 further comprising: performing a remedial operation to correct a microannulus.
 15. The method of claim 10, wherein optically interacting a material of interest and at least one integrated computational element occurs over a period of time and a plurality of output signals are produced each corresponding to both a time and the characteristic of the material of interest.
 16. A method comprising: optically interacting a material of interest and at least one integrated computational element, thereby generating an output signal corresponding to a characteristic of the material of interest, the material of interest comprising at least one selected from the group consisting of a cement sheath disposed about and in contact with at least a portion of an exterior surface of a casing, a displacement composition disposed between the cement sheath and the exterior surface of the casing, and any combination thereof; analyzing for an indicator of microannulus formation; and performing a remedial operation to correct a microannulus.
 17. The method of claim 16, wherein the characteristic of the material of interest is at least one selected from the group consisting of chemical composition, impurity content, pH, viscosity, density, ionic strength, total dissolved solids, salt content, porosity, opacity, bacteria content, particle size distribution, color, temperature, hydration level, and an analyte oxidation state.
 18. The method of claim 16, wherein optically interacting a material of interest and at least one integrated computational element occurs over a period of time and a plurality of output signals are produced each corresponding to both a time and the characteristic of the material of interest.
 19. The method of claim 16, wherein the at least one integrated computational element is coupled to at least one selected from the group consisting of the casing, a centralizer operably coupled to the casing, a casing shoe operably coupled to the casing, and a collar operably coupled to the casing. 